1. Field of the Invention
The present invention relates to a fiber-waveguide self alignment technique and, more particularly, to an alignment technique wherein one or more fibers are held in silicon V-grooves and mated in an overlap fashion with the waveguide substrate such that five of the six possible degrees of freedom are automatically aligned.
2. Description of the Prior Art
Packaging has become a key issue in evaluating the manufacturability and reliability of optical devices. A significant part of the packaging problem is due to the stringent alignment tolerances required for coupling between the devices and optical fibers. To date, most applications (i.e.; lasers, detectors) have required the alignment of only a single fiber. However, with the advent of integrated optical devices, the need has arisen to align linear arrays of fibers to devices. One prior art technique for accomplishing array alignment is disclosed in U.S. Pat. No. 4,217,032, issued to S. K. Sheem on Aug. 12, 1980. The Sheem technique utilizes a two-dimensional, intersecting groove pattern formed in a silicon substrate wherein a groove in one direction is deeper than an intersecting groove, and an alignment fiber rests in the deep groove. The shallow groove accommodates an optical fiber, where the optical fiber is sized to contact the alignment fiber. The alignment fiber is tapered so that as it slides along the groove, it raises or lowers the optical fiber to a level which yields the maximum optical transmission. This alignment technique becomes extremely time consuming when a large array of optical fibers must be individually adjusted.
The coupling of a single mode optical fiber to a waveguide requires an extremely accurate alignment, much more so than is the case for multimode fibers. For example, for an amplitude half width at e.sup.-1, a radial offset of one micron would result in an excess loss of 0.3 dB. U.S. Pat. No. 4,164,363 issued to H. Hsu on Aug. 14, 1979 discloses a single mode fiber-to-channel waveguide end-fire coupler. Here, a single mode fiber is held within a capillary tube and adjusted by a micropositioner for greatest light output. The fiber is then secured by an epoxy to one end of a channel waveguide. The two ends are then secured in place in a slot in the capillary tube which prevents rotation of the waveguide relative to the single fiber. As with the above-described Sheem arrangement, the Hsu technique requires active alignment, by monitoring and maximizing the optical transmission. This method also becomes extremely time consuming when a large array of fibers must be aligned.
An alternative alignment arrangement which does not require individual alignment is disclosed in U.S. Pat. No. 4,186,997 issued to W. L. Schumacher on Feb. 5, 1980. The Schumacher disclosure relates to a method and apparatus for connecting optical waveguides in coincident alignment, and features a connector divided into intermating sections, with each section in the form of an open box configuration provided with a projecting tongue for intermating with other waveguide sections. Schumacher, however, does not discuss fiber-waveguide interconnections, nor any method which reduces the number of degrees of freedom which must simultaneously be aligned.
There remains a need, therefore, for a fiber-waveguide alignment technique capable of aligning arrays of both multimode and single mode fibers which can simplify the alignment process, that is, which reduces the number of degrees of freedom which must be actively adjusted, that is, adjusted while monitoring and maximizing the optical transmission.